Until the End of Time: Mind, Matter, and Our Search for Meaning in an Evolving Universe

by Brian Greene

Without an environment chock-full of low-entropy ordered structures, we humans would not be here to notice.

Heat and Entropy

To absorb heat is to absorb energy that is carried by random molecular motion. That energy, in turn, drives the receiving molecules to move more quickly or spread more widely, thus contributing to an increase in entropy. The conclusion, then, is that to shift entropy from here to there, heat needs to flow from here to there. And when heat flows from here to there, entropy shifts from here to there. In short, entropy rides the wave of flowing heat.

Heat and the Second Law of Thermodynamics

The Entropic Two-Step

You Are a Steam Engine

3

ORIGINS AND ENTROPY

From Creation to ...

If the second law of thermodynamics burdens the universe with a relentless increase in disorder, how can nature so readily produce exquisitely configured, highly ordered structures, from atoms and molecules, to stars and galaxies, to life and mind?

Sketching the Big Bang

Here is the modern cosmological account that has emerged: Some fourteen billion years ago, the entire observable universe—all that we can see using the most powerful telescopes imaginable—was compressed into a stupendously hot, incredibly dense nugget, which then rapidly expanded. Cooling as it swelled, particles gradually slowed their frenzied motion and aggregated into clumps, which over time formed stars, planets, all manner of gaseous and rocky debris scattered across space—and us.

Repulsive Gravity

More precisely, Guth’s calculations revealed that if a tiny region, perhaps as small as a billionth of a billionth of a billionth of a meter across, was suffused with a certain type of energy field (called the inflaton field, with the missing “i” being an intentional if quirky naming convention), and if the energy was distributed uniformly, like steam whose density is the same throughout a sauna, the repulsive gravitational push would be so forceful that the speck of space would inflate explosively, almost instantaneously stretching to as large as the observable universe, if not far larger.

In the early 1980s, Soviet physicist Andrei Linde and the American duo Paul Steinhardt and Andreas Albrecht took Guth’s handoff and ran with the concept, developing the first fully viable versions of inflationary cosmology.

The Afterglow

Inflationary cosmology refines the prediction of an afterglow by taking into account quantum mechanics, the laws developed in the early decades of the twentieth century to describe physical processes playing out in the microworld. Since we’re focused on the entire universe, something big, you might think the preoccupation of quantum physics with all things small would make it irrelevant. And if it weren’t for inflationary cosmology, your intuition would be on the mark. But much as stretching a piece of spandex reveals the intricate pattern of its stitches, stretching space through a burst of inflationary expansion reveals quantum features usually cordoned off in the microworld. In essence, inflationary expansion reaches into the microworld and stretches quantum features clear across the sky.

Much as you know the implications of Newtonian physics in your bones—you can quickly grab a falling glass,

Which one should NEVER do.

Although I described the inflaton’s value as being uniform, taking on the same value at all locations within the inflating patch of space, quantum uncertainty fuzzes this out. Uncertainty overlays quantum jitters on the classical uniformity, resulting in the field’s value, and hence its energy, being a tiny bit higher here and a tiny bit lower there.

The calculations revealed that the stretched-out quantum jitters result in a distinct pattern of temperature variations across space, a cosmological fingerprint available for astronomical forensics. Indeed, since the early 1990s, a sequence of telescopes deployed above the distortions caused by earth’s atmosphere have confirmed the predicted pattern of temperature variations with ever-greater precision.

But it would be too strong to conclude that the observations prove that a burst of inflationary expansion happened. When focusing on cosmological events that took place billions of years ago, at an energy scale likely millions of billions of times what we can probe in the laboratory, the best we can do is piece together observations and calculations to build confidence in our explanations. If an inflationary burst were the only way to understand the cosmological data then our confidence would head closer to certainty, but over the years imaginative scientists have developed alternative approaches (we will encounter one of these in chapter 10).

The Big Bang and the Second Law

Inflation requires a list of ingredients that includes space, time, the cosmic fuel driving the expansion (the inflaton field), as well as the whole technical apparatus of quantum mechanics and general relativity, which themselves rest upon mathematics from multivariable calculus and linear algebra to differential geometry. There is no known principle that singles out these particular physical laws, articulated using these particular mathematical constructs, as the inevitable starting point for explaining the universe.

Instead, we physicists use observation and experiment, together with a hard-to-describe intuitive mathematical sensibility, to guide us toward particular physical laws. We then analyze the laws mathematically to determine which environmental conditions in the earliest moments of the universe, if any, would have sparked the rapid expansion of space. Upon finding, happily, that there are such conditions, we postulate that they held near the big bang and we use the equations to determine what subsequently would have happened.

A low-entropy configuration is special. It is unusual. It calls out for an explanation for how such an ordered state of affairs came to be.

By what force or process did the early universe acquire low entropy?

But what or who arranged the special low-entropy configuration of the early universe? Without a complete theory of cosmic origins, science can’t provide an answer.

While none of this addresses the most fundamental questions of origin (the origin of space, or time, or fields, or mathematics, and so on), it shows how a chaotic environment can produce the special, ordered, low-entropy conditions inflation requires. When a tiny speck of space finally makes the statistically unlikely leap to low entropy, repulsive gravity jumps into action and propels it into a rapidly expanding universe—the big bang.

The Origin of Matter and the Birth of Stars

Hurdles on the Path Toward Disorder

Gravity, Order, and the Second Law

As the core of such a gas cloud contracts under the pull of gravity, its entropy decreases, but in the process it releases heat that causes the entropy of the surroundings to increase. A local region of order is created within an environment that undergoes a more than compensating surge in disorder.

Fusion, Order, and the Second Law

When gravity’s influence is minimal, the second law drives a system toward homogeneity. Things spread out, energy diffuses, entropy increases.

But when there’s enough matter for gravity’s influence to be significant, the second law undertakes a rapid U-turn, and drives the system away from homogeneity. Matter clumps here and spreads out there. Energy concentrates here and diffuses there. Entropy decreases here and increases there.

When there’s enough gravity—enough sufficiently concentrated stuff—ordered structures can form.

When atomic nuclei fuse—as in the sun, where hydrogen nuclei fuse into helium billions and billions of times each second—the result is a more complex, more intricately organized, lower-entropy atomic cluster. In the process, some of the mass of the original nuclei is converted into energy (as prescribed by E = mc2), mostly in the form of a burst of photons that heats the star’s interior and powers the release of light from the star’s surface. And it is through such fiery starlight, which is itself a torrent of outward streaming photons, that the star transfers copious quantities of entropy to the environment.

Thus, although gravity is the vital force in the formation of a star and in maintaining a stable stellar environment, for billions of years it’s the nuclear force that’s on the front line, spearheading the entropic charge. From this perspective, gravity’s role shifts from leading protagonist to indispensable partner in a long duet.

4

INFORMATION AND VITALITY

From Structure...

Nested Stories

Nevertheless—and this is key—these better-suited human-level stories must be compatible with the reductionist account. We are physical creatures subject to physical law. And so there’s little to be gained by physicists clamoring that theirs is the most fundamental explanatory framework or from humanists scoffing at the hubris of unbridled reductionism. A refined understanding is gleaned by integrating each discipline’s story into a finely textured narrative.

The Origin of the Elements

A flurry of analyses have determined that neutron-star collisions produce heavier elements more efficiently and abundantly than supernova explosions, and so it may be that the majority of the universe’s heavy elements were produced through these astrophysical smashups.

The Origin of the Solar System

What we can say with more confidence is that some 4.7 billion years ago a supernova shock wave likely plowed through a cloud containing hydrogen, helium, and small quantities of more complex atoms, compressing part of the cloud, which, now being denser than its surroundings, exerted a stronger gravitational pull and thus began to draw material inward. Over the next few hundred thousand years, this region of the gas cloud continued to contract, rotating slowly at first and then more rapidly, like a graceful skater pulling in her arms while spinning. And much as the spinning skater experiences an outward pull (which splays out any loose fringe on the skater’s costume), so did the spinning cloud, which spread and flattened its outer regions into a rotating disk, which surrounded a smaller spherical region at the core. During the following fifty to one hundred million years, the gas cloud then performed a slow and steady rendition of the gravitational entropic two-step discussed in chapter 3: The gravitational force squeezed the spherical core, which grew ever hotter and denser, while the surrounding material cooled and thinned. The entropy of the core decreased; the entropy of the surroundings offset that by a more than compensating increase. Ultimately, the core’s temperature and density crossed the threshold for igniting nuclear fusion. The sun was born.

Young Earth

The smashup with Theia is the likely cause of earth’s cant.

Life, Quantum Physics, and Water